In U.S. Pat. No. 3,187,440, entitled "Dynamic Wheel Alignment Testing Apparatus", and assigned to the same assignee as the present invention, a wheel testing apparatus is described for determining various interrelated angles pertinent to the alignment of the front suspension of a vehicle. The dynamic testing apparatus described therein includes at least a front roll and a rear roll on which a vehicle wheel is placed. The rolls are rotated and the rotation thereof rotates the wheel and tire. Each of the rolls is movable along its axis according to forces applied by the rotating wheel on the rolls. These axial wheel forces are directly proportional to the toe angle and camber angle of the wheel. Toe-in may be broadly defined as the inward slanting of the wheel toward the front. Camber may be broadly defined as the inward sloping of the wheel toward the bottom. The axial displacement of the rolls due to the wheel forces is then coupled to rotary hydraulic valves which control a hydraulic, closed loop servo system. The servo system hydraulics rotates the testing apparatus about a vertical axis in the determination of the toe angle and tilts the top frame of the testing apparatus about a horizontal axis in the determination of the camber angle of the wheel. The testing apparatus or its top frame are rotated or tilted until the forces on the rolls equal zero. The amount of rotation of the testing apparatus about a vertical axis is directly related to the toe angle of the wheel. The amount of rotation of the testing apparatus about the horizontal axis is directly related to the camber angle of the wheel. Transducers for sensing the position of the wheel testing apparatus are mounted thereon and are connected to display meters through suitable electronic hardware.
The wheel testing apparatus of U.S. Pat. No. 3,187,440 accurately determines the toe angle and camber angle of a vehicle wheel. If the angles are not within the manufacturer's specifications, an alignment operator can adjust the toe angle or camber angle while the rolls and wheel are rotating and by observing the changes on the display meters until the toe angle and camber angle are within the proper range. This method of alignment is generally satisfactory. However, the manufacture and use of front wheel drive vehicles has significantly increased. The front wheel drive system, in contrast to the rear wheel drive, does not afford the same amount of space for the alignment operator to make any necessary toe and camber adjustments. As a consequence, an alignment operator, who is adjusting the toe and camber angles of a front wheel drive system, is not afforded the same degree of safety. In order to maximize safety, the present invention is provided to enable the operator to adjust pertinent wheel angles of the vehicle while the rolls are stopped. The alignment operator need not be concerned about the moving rolls while adjusting the toe and camber angles in the relatively less space provided in a front wheel drive vehicle.
Generally speaking, it is not uncommon to align the front wheels of a vehicle while the wheels are not rotating. This method of alignment can be defined as static alignment, in direct contrast to the dynamic mode of determining wheel angles are disclosed in U.S. Pat. No. 3,187,440. It is, however, recognized that there are significant differences between the alignment of a wheel in its static mode versus its dynamic mode. In addition, the dynamic mode of determining wheel angles provides a more worthwhile indication of the vehicle alignment. Based on these premises, the dynamic mode of alignment was conceived. The present invention further improves the dynamic wheel alignment capability by combining the dynamic mode of determining the appropriate wheel angles with a static mode of setting or aligning the front wheels so that the toe angle and camber angle are within the desired range.